1. Technical Field
This invention relates to an electrical junction box.
2. Background Art
Heretofore, an example of an electrical junction box has been known in JP HEI 8(1996)-274421 A. This electrical junction box contains a circuit board in a casing. A heat generation part, such as a power transistor or the like, is mounted on the circuit board. A lead of the heat generation part is connected through a solder to a bus bar disposed on the circuit board.
FIG. 13 schematically shows a heat transmission path in a conventional electrical junction box. As shown in FIG. 13, heat generated from a heat generation part 110 during electrical conduction is transmitted from a lead 111 of the heat generation part 110 through a solder 112 to a bus bar 113. The heat transmitted to the bus bar 113 is radiated into air 114 in a casing 115, the heat is then transmitted from the air 114 to the casing 115. The heat transmitted to the casing 115 is then radiated from an outer side surface of the casing 115 to a casing outside 116. Thus, it has been expected to effectively radiate the heat generated from the heat generation part 110 to the casing outside 116.
However, in junction boxes based on the above construction, the heat transmitted to the bus bar 113 is radiated through a layer of air 114 in the casing 115. Since air 114 has a relatively low coefficient for heat conduction, heat accumulates in the casing 115 resulting in a temperature increase in the casing 115. Consequently, an electronic part mounted on the circuit board may malfunction, or the reliability in the solder connection may be lowered.
In view of the above problems, an object of the present invention is to provide an electrical junction box that can restrain a temperature from increasing in a casing.